Not applicable.
Not applicable.
The present invention relates generally to methods and apparatus for separating solid particles from a fluid. More specifically, the present invention relates to methods and apparatus that use cylindrical vessels to separate contaminants from a fluid. Still more specifically, the present invention relates to cylindrical vessels that use centrifugal force and gravity to separate solid contaminants from a fluid.
The separation of solid particles from fluids is an important consideration in many industries from heavy construction to wastewater treatment. One industry in which the separation of solids from fluids is very important is rotary drilling. Rotary drilling techniques are used extensively in drilling hydrocarbon wells, water wells, and mining applications. In rotary drilling, a fluid, known as drilling mud, is circulated down a drill string, through a drill bit, and back up the borehole to the surface. The drilling mud acts as a lubricant for the drill bit and carries cuttings from the bottom of the borehole to the surface.
Most rotary drilling applications also rely on the drilling mud to control underground pressures developed by the formation fluids. Therefore, the density of the drilling mud is closely maintained in order to control the hydrostatic pressure that the mud exerts at the bottom of the well. If the mud is too light, formation fluids, which are at higher pressures than the hydrostatic pressure developed by the drilling mud, can enter the wellbore and flow uncontrolled to the surface, possibly causing a blowout. If the mud is too heavy, then the hydrostatic pressure exerted at the bottom of the wellbore can reduce the rate at which the drill bit will drill the hole. Thus, the control of the solids content of the drilling fluid is very crucial to the overall efficiency and safe operation of the rig.
The cleaning and conditioning of drilling mud at the surface normally includes a series of solids control equipment, which may include shale shakers that remove large particles from the drilling mud, desilters and/or desanders that remove smaller particles, degassers that remove entrained gas, mud-gas separators to remove free gas, and dewatering equipment to reclaim drilling fluid while reducing hauloff. Clarifying tanks are also used in the cleaning and conditioning of drilling mud and, depending on their specific design, can be used for a variety of functions, such as large particle removal and fine solids dewatering.
One type of clarifying tank utilizes a cylindrical vessel into which drilling fluid is injected through a tangential nozzle, which causes the fluid to spin inside the tank. This spinning motion creates a vortex, which imparts centrifugal forces onto any solid particles within the fluid. These centrifugal forces move the particles away from the center of the tank, thus leaving a relatively clean fluid at the center. Any free gas will also migrate to the center of the vortex. A centrally located outlet near the top of the tank can then be utilized to withdraw the substantially clean fluid from the tank. The solid particles that are pushed to the outside of the circulating fluid are allowed to fall to the base of the tank where they can be collected and removed for recycling or disposal.
Some clarifying tanks have conical bottoms that collect solids and direct the particles toward a centrally located outlet where they can be removed from the tank. The outlet, typically located at the apex of the conical bottom, is often fitted with a valve that can be opened and closed to regulate the flow of solids exiting the tank. It is often desired to remove the collected solid particles from the tank without removing an excess of fluid. The valve can be used to control the characteristics of the material that is removed from the tank. One problem with some prior art configurations is that the opening and closing of the valve must be closely monitored to ensure the efficient removal of solids from the tank. If the valve remains open for too long, all of the accumulated solids may flow out of the tank and excess fluid will be lost through the outlet. If the valve is left closed for too long, the solids will build up in the bottom of the tank and may not flow once the valve is opened.
Thus, there remains a need in the art for methods and apparatus for separating solid material from a fluid. Therefore, the embodiments of the present invention are directed to methods and apparatus for separating solids that seek to overcome these and other limitations of the prior art.
Accordingly, there are provided herein methods and apparatus for separating solid particles from a fluid. One embodiment includes a tank in which solid particles are allowed to settle out of a fluid and are collected in a conical chamber at the bottom of the tank. The conical chamber has an outlet and may include a conical auger within the chamber to move the solid particles through the outlet. The tank preferably has a tangential inlet that creates a fluid circulation in order to exert centrifugal forces fluid in order to increase the separation of the heavy solid particles from the relatively light fluid. The tank may also have a static coalescing spiral on the inner wall that helps small particles combine to form larger particles that settle faster out of the fluid.
In some applications, the solid particles that settle out of the fluid and fill the conical chamber may form a plug between the tank and the conical chamber that prevents the free flow of fluid into the conical chamber. The conical auger rotates moves a portion of the solid particles through the outlet with each rotation. The solid particles moved by the conical auger are further compressed as they travel toward the outlet.
An alternative embodiment includes a method of separating solid particles from a fluid by settling the particles out of the fluid in a tank and removing the settled solid particles from the bottom of the tank with a conical auger. The solid particles may also be compressed by the conical auger as the particles are moved toward the outlet. This additional compression of particles further helps to control the liquid content of the material removed from the tank. The material removed from the tank may also be controlled by varying the rotational speed of the conical auger. As the speed of the conical auger increases, more solids are removed from the tank. In certain embodiments, the rotational speed of the conical auger may be varied depending on the torque required to rotate the conical auger.
Depending somewhat on the viscosity of the material removed from the tank, certain embodiments may use additional material handling equipment to move the material once it has left the system. Certain embodiments may use a positive displacement pump or a horizontal screw-type auger to further move the solid material away from the tank and position the material for further processing or handling. Some applications using this additional handing equipment outside the clarifying tank may operate without the use of an internal conical auger.
Alternative embodiments may also provide for the collection of any free gas that may be contained within the fluid by way of a degassing system disposed at the top of the tank. Free gas in the fluid entering the tank will, when subjected to centrifugal forces, tend to collect at the center and move to the top of the tank along with the substantially clean fluid. The degassing system provides a controlled space where gas can be removed from the system free of substantial quantities of liquids. Preferred embodiments of the degassing system provide a return line for returning excess liquid to the system.
Thus, the present invention comprises a combination of features and advantages that enable it to substantially increase the efficiency of separating solid particles from a liquid. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings.